The present invention relates to an oscillator circuit, and more particularly, to an oscillator circuit that generates an oscillator signal supplied to a charge pump circuit of an internal power generator circuit.
FIG. 1 is a schematic block diagram of a conventional internal power generator circuit built in a semiconductor device. The internal power generator circuit acts as a boosted power generator circuit 91 for boosting an external or internal supply voltage VDD to generate a boosted voltage VPP.
The boosted power generator circuit 91 includes a first and a second detector circuit 92, 93 for detecting the boosted voltage VPP; a first and a second oscillator circuit 94, 95; a signal synthesizer circuit 96; and a charge pump circuit 97. The boosted power generator circuit 91 has an active mode in which a current is supplied with a relatively large driving performance, and a standby mode in which a current is supplied with a relatively small driving performance.
The active mode will be first described.
In the active mode, the first detector circuit 92 is activated by an activation signal xcfx86. The first detector 92 is a detector circuit for the active mode which has relatively large current consumption and operates at a relatively high reaction speed. The first detector circuit 92 detects the boosted voltage VPP in the active mode and generates a detection signal DET-A when the boosted voltage VPP decreases to a voltage equal to or smaller than a predetermined voltage. The first oscillator circuit 94 receives the detection signal DET-A from the first detector circuit 92, and generates an oscillator signal OSC-A for the active mode which has a relatively short period (for example, several tens of nanoseconds (ns)) (i.e., a relatively high oscillating frequency).
The signal synthesizer circuit 96 receives the oscillator signal OSC-A from the first oscillator circuit 94, and generates an oscillator signal OSC in accordance with the oscillator signal OSC-A for the active mode. The charge pump circuit 97 performs a charge pump operation following the period of the oscillator signal OSC to boost the external or internal supply voltage VDD to generate the boosted voltage VPP.
Next, the standby mode will be described.
The second detector circuit 93 is activated without fail whenever the device is applied with the supply voltage VDD, not only in the standby mode. The second detector circuit 93 is a detector circuit for the standby mode which has relatively small current consumption and operates at a relatively low reaction speed. The second detector circuit 93 is activated at all times irrespective of whether the device is in the active mode or in the standby mode.
The second detector circuit 93 detects the boosted voltage VPP, and generates a detection signal DET-S when the boosted voltage VPP decreases to a voltage equal to or smaller than a predetermined voltage. The second oscillator circuit 95 receives the detection signal DET-S from the second detector circuit 93, and generates an oscillator signal OSC-S for the standby mode which has a relatively long period (for example, several hundreds of nanoseconds (ns)) (i.e., a relatively low oscillating frequency).
The signal synthesizer circuit 96 receives the oscillator signal OSC-S for the standby mode from the second oscillator circuit 95, and generates an oscillator signal OSC in accordance with the oscillator signal OSC-S for the standby mode. The charge pump circuit 97 performs a charge pump operation following the period of the oscillator signal OSC to boost the external or internal supply voltage VDD to generate the boosted voltage VPP.
As described above, the boosted power generator circuit 91 operates at different frequencies in the active mode and standby mode. In the active mode, the boosted power generator circuit 91 supplies a larger current than in the standby mode to generate the boosted voltage VPP. In the standby mode, the boosted power generator circuit 91 consumes a smaller current to limit its power consumption.
In the active mode, the first oscillator circuit 94 as well as the second oscillator circuit 95 are activated. However, since the first and second oscillator circuits 94, 95 are asynchronous to each other, a pulse having a shorter period than the period of the oscillator signals OSC-A, OSC-S of the oscillator circuits 94, 95 may be generated in some cases. Such a pulse may cause a malfunction of the charge pump circuit 97. Specifically, a shorter pulse period would result in a failure in a sufficient charge pump operation, a reduced current supply capability, or increased power consumption.
To solve this problem, it is contemplated to separately provide a charge pump circuit for the active mode and a charge pump circuit for the standby mode. However, since the charge pump circuit has a relatively large circuit area, separately provided charge pump circuits would result in an increased semiconductor die size and increased power consumption.
It is an object of the present invention to provide an oscillator circuit which generates an oscillator signal that ensures the generation of a stable internal supply voltage.
In a first aspect of the present invention, a method of controlling an oscillator circuit having a periodic circuit which includes a switch circuit is provided. The method includes the steps of operating the periodic circuit using the switch circuit in response to a first control signal when the first control signal is in a first state to generate a first oscillator signal having a first frequency, and operating the periodic circuit using the switch circuit in response to a second control signal when the first control signal is in a second state to generate a second oscillator signal having a period synchronized to a period of the second control signal having a second frequency.
In a second aspect of the present invention, a method of controlling an oscillator circuit having a periodic circuit which includes a switch circuit is provided. The method includes the steps of operating the periodic circuit in response to a first control signal using the switch circuit to generate a first oscillator signal synchronized in phase to the first control signal, and operating the periodic circuit in response to a second control signal using the switch circuit to generate a second oscillator signal synchronized in phase to the second control signal.
In a third aspect of the present invention, an oscillator circuit is provided that includes a synthesizer for synthesizing a first control signal with a pulse signal to generate a synthesized signal, a pulse generator circuit connected to the synthesizer for generating a pulse signal in response to a second control signal and supplying the pulse signal to the synthesizer, a control circuit connected to the synthesizer for generating a switch control signal in accordance with the synthesized signal, and a periodic circuit connected to the control circuit, and including a switch circuit responsive to the switch control signal. The periodic circuit generates one of a first oscillator signal having a first frequency and a second oscillator signal having a second frequency in accordance with an operation of the switch circuit.
In a fourth aspect of the present invention, an oscillator circuit is provided that includes a first pulse generator circuit for generating a first pulse signal in response to a first control signal, a second pulse generator circuit for generating a second pulse signal in response to a second control signal, a synthesizer connected to the first and second pulse generator circuits for synthesizing the first pulse signal and the second pulse signal to generate a synthesized signal, a control circuit connected to the synthesizer for generating a switch control signal in accordance with the synthesized signal, and a periodic circuit connected to the control circuit, and including a switch circuit responsive to the switch control signal. The periodic circuit generates one of a first oscillator signal corresponding to the first control signal and having a first frequency and a second oscillator signal corresponding to the second control signal and having a second frequency in accordance with an operation of the switch circuit.
In a fifth aspect of the present invention, a method of controlling an internal power generator circuit is provided. The internal power generator circuit includes an oscillator circuit having a periodic circuit including a switch circuit, and a charge pump circuit connected to the oscillator circuit. The method includes the steps of operating the periodic circuit in response to a first control signal using the switch circuit, when the first control signal is in a first state, to generate a first oscillator signal having a first frequency, generating a voltage in accordance with the first oscillator signal using the charge pump circuit, operating the periodic circuit in response to a second control signal using the switch circuit, when the first control signal is in a second state, to generate a second oscillator signal having a period synchronized to a period of the second control signal having a second frequency, and generating the voltage in accordance with the second oscillator signal using the charge pump circuit.
In a sixth aspect of the present invention, a method of controlling an internal power generator circuit is provided. The internal power generator circuit includes an oscillator circuit including a periodic circuit having a switch circuit, and a switch control circuit for controlling the switch circuit, and a charge pump circuit connected to the oscillator circuit. The method includes the steps of controlling the switch circuit in response to a first control signal by the switch control circuit to operate the periodic circuit to generate a first oscillator signal having a period synchronized to a period of the first control signal, generating a voltage in accordance with the first oscillator signal using the charge pump circuit, controlling the switch circuit in response to a second control signal by the switch control circuit to operate the periodic circuit to generate a second oscillator signal having a period synchronized to a period of the second control signal, and generating the voltage in accordance with the second oscillator signal using the charge pump circuit.
In a seventh aspect of the present invention, an internal power generator circuit is provided that includes a first oscillator circuit and a charge pump circuit. The first oscillator circuit includes a synthesizer for synthesizing a first control signal with a pulse signal to generate a synthesized signal, a pulse generator circuit connected to the synthesizer for generating a pulse signal in response to a second control signal and supplying the synthesizer with the pulse signal, a control circuit connected to the synthesizer for generating a switch control signal in accordance with the synthesized signal, and a periodic circuit connected to the control circuit and including a switch circuit responsive to the switch control signal. The periodic circuit generates one of a first oscillator signal having a first frequency and a second oscillator signal having a second frequency in accordance with an operation of the switch circuit. The charge pump circuit is connected to the periodic circuit and generates a voltage in accordance with one of the first oscillator signal and the second oscillator signal.
In an eighth aspect of the present invention, an internal power generator circuit is provided that includes a first oscillator circuit and a charge pump circuit. The first oscillator circuit includes a first pulse generator circuit for generating a first pulse signal in response to a first control signal, a second pulse generator circuit for generating a second pulse signal in response to a second control signal, a synthesizer connected to the first and second pulse generator circuits for synthesizing the first pulse signal and the second pulse signal to generate a synthesized signal, a control circuit connected to the synthesizer for generating a switch control signal in accordance with the synthesized signal, and a periodic circuit connected to the control circuit, and including a switch circuit responsive to the switch control signal. The periodic circuit generates one of a first oscillator signal corresponding to the first control signal and having a first frequency and a second oscillator signal corresponding to the second control signal and having a second frequency in accordance with an operation of the switch circuit. The charge pump circuit is connected to the periodic circuit and generates a voltage in accordance with one of the first oscillator signal and the second oscillator signal.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.